Mobile radio communication system

ABSTRACT

A mobile radio communication system which does not need an omnidirectional channel for both a base station and a mobile station to track each other and uses only a narrow beam channel and can reduce a tracking time than before for an adjacent base station and a mobile station to search each other while a visiting area base station and the mobile station are communicating in the overlapped area. The base station and the mobile station comprise a unit for transmitting and receiving in forward or reverse channel, in different frequency, in different tracking channel using a narrow beam. Both the mobile station and the visiting area base station search the location each other, and after searched, they assign the frequency and the beam used in the tracking channel. At the same time, by comprising a searching slot in an information channel to search an adjacent base station while communicating with the visiting area base station, a tracking of other adjacent base station can be performed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of pending application Ser. No.09/274,308, filed Mar. 23, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to, in a mobile radio communication systemin which a base station and a mobile station under control of the basestation have a tracking channel for tracking each other by a narrowbeam, a tracking method between the mobile station and the base station(namely, a visiting area base station as it controls an area which themobile station moves around), and a method of searching an adjacent basestation while the mobile station communicates with the visiting areabase station.

2. Description of Related Art

FIG. 11 illustrates a configuration of a conventional “mobile radiocommunication system” described in Japanese Patent Application Laid-openNo. Hei8-8814. In FIG. 11, reference numerals 1101 a, 1101 b and 1101 cdenote mobile stations; 1102 a base station; and 1103 an antenna of thebase station 1102.

Next, the operation will be explained. In FIG. 11, different frequencychannels are assigned to each mobile station. For example, aninformation channel f1, f2 and f3 are assigned to a mobile station 1101a, 1101 b and 1101 c, respectively. The mobile radio communicationsystem further comprises a frequency channel f0 common to the basestation for transmitting a beam direction information of antennadirectivity. As shown in FIG. 12, the base station 1102 controls atransmitting direction omnidirectionally varying a bearing angle θhorizontally as θ1, θ2 and θ3. At the same time, as shown in FIG. 13,the base station 1102 controls a transmitting directionomnidirectionally varying a depression angle φ vertically as φ1, φ2 andφ3.

The mobile station 1101 a or the like measures the above bearing angleand depression angle information as well as their receiving levels atany time. The mobile station 1101 a or the like identifies a directionof a maximum measured receiving level as a direction of the basestation, and transmits again an optimal bearing angle, an optimaldepression angle, the receiving level of the optimal bearing angle andthe receiving level of the optimal depression angle.

The base station 1102 determines a transmitting level based on thereceiving level of the optimal bearing angle and the receiving level ofthe optimal depression angle transmitted from the above mobile station1101 a or the like, and controls the transmitting level to preventinterference among the base station 1102 and other base stations.

But, when the mobile station approaches to a boundary between the basestation 1102 and an adjacent base station, there is a problem in that itis becoming difficult for the mobile station to select a beam from thebase station because of a interference wave coming from a plurality ofthe adjacent base stations.

In “A radio communication system” described in Japanese PatentApplication Laid-open No. Hei5-276084, a mobile radio communicationsystem employing a directive antenna and a phased array antenna in amobile station and a base station is shown, and further, two methods aredescribed as a method of irradiating an omnidirectional pattern to startspeech, one of the two methods is a method of providing a connectionspecific phased array antenna, and the other method is a method ofadjusting a phase shifter of the array itself appropriately.

When one of the station performs a omnidirectional irradiation and theother station detects the irradiation in the above method, the otherstation performs a directive irradiation in the direction of thedetected direction and then modifies a transmitting direction of adirective antenna at any time based on an information of a phase valueand an amplitude value received by the phased array antenna. Further, amethod is described that the above method enables a channel switchingwhen the mobile station moves across the area of the other base station.

But, the above method always needs the omnidirectional irradiation, andneeds to comprise both irradiation systems including the omnidirectionalirradiation and the narrow beam irradiation.

As mentioned above, in conventional mobile radio communication system,when the mobile station approaches to a boundary between the basestation and an adjacent base station, there is a problem in that it isbecoming difficult for the mobile station to select a beam from the basestation because of a interference wave coming from a plurality of theadjacent base stations.

In another conventional mobile radio communication system, there is aproblem in that both of the omnidirectional channel and the narrow beamchannel are needed to start a speech.

Further, in an overlapped area in which a mobile station cancommunicates with a plurality of base stations, both of an adjacent basestation which may be handovered and a mobile station need a trackingchannel different from the above channel. In the overlapped area, thereis a problem in that the adjacent base station and the mobile stationset the tracking channels of different frequency and different beam toavoid the interference and track each other, resulting in increasingtracking time.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the above problems, andto provide a mobile radio communication system which does not need anomnidirectional channel for both a base station and a mobile station totrack each other and uses only a narrow beam channel. Another object ofthe present invention is to provide a mobile radio communication systemwhich reduces a tracking time than before for an adjacent base stationand a mobile station to search each other while a visiting base stationand the mobile station are communicating in the overlapped area.

According to a first aspect of the present invention, there is provideda mobile communication system comprising an mobile station; at least onebase station including an visiting area base station which controls anarea in which the base station visits; and a tracking channel being usedby both the mobile station and the at least one base station fortracking each other using a narrow beam, wherein a transmitting side ofthe base station has a control means for controlling a direction of atransmitting beam, and a receiving side of the mobile station has acontrol means for varying a receiving direction.

According to a second aspect of the present invention, there is provideda mobile communication system, comprising: an mobile station; anvisiting area base station controlling an area in which the base stationvisits; an adjacent base station being adjacent to the visiting areabase station; and a base station control unit controlling the visitingarea base station and the adjacent base station, wherein the mobilestation receives a tracking channel by a searching slot during thevisiting area base station and the mobile station are communicating eachother using an information channel, where the tracking channel includesa base station identifier transmitted from the adjacent base station,the mobile station transmits a mobile station identifier and a controlinformation including a location information and the base stationidentifier of the adjacent base station obtained from the trackingchannel to the visiting area base station, and the visiting area basestation transmits the control information to the adjacent base stationvia the base station control unit.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of the embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of the present mobile radiocommunication system.

FIG. 2 is a conceptual diagram showing an example of controlling adirection of a receiving angle in a mobile station.

FIG. 3 is a flowchart showing a flow from a tracking processing to astarting of a communication in a base station.

FIG. 4 is a flowchart showing a flow from a tracking processing to atransmitting in a mobile station.

FIG. 5 is a sequence diagram showing a sequence from a trackingprocessing to a communicating state between a mobile station and a basestation.

FIGS. 6A and 6B are configuration diagrams of tracking slots and controlslots in information channels.

FIG. 7 is an illustrative diagram of an information channel incommunicating between a mobile station and a visiting area base station,and a searching method by a tracking slot between the mobile station andan adjacent base station.

FIG. 8 is a sequence diagram showing a sequence of tracking an adjacentbase station being searched.

FIG. 9 is an example of configuration diagram of an information channelbetween a mobile station and a plurality of a base station at the timeof handover.

FIG. 10 is a sequence diagram showing an alteration sequence from acommunicating state to a tracking state, and a sequence at the time ofpower off or entering an adjacent base station area.

FIG. 11 is a conventional configuration diagram of a control systemusing a narrow beam.

FIG. 12 is a conventional transmitting control of a narrow beam in thedirection of a bearing angle in a base station.

FIG. 13 is a conventional control of a narrow beam in the direction of adepression angle in a base station.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described below withreference to the accompanying drawings. It is noted that the samereference symbols in the drawings denote the same or correspondingcomponents.

Embodiment 1

FIG. 1 shows a configuration diagram of the present mobile radiocommunication system. In FIG. 1, reference numerals 101 a-101 g denotemobile stations; 102 a-102 e base stations include the mobile stations101 a or the like and connect the mobile stations 101 a or the like byradio wave; 103 a base station control unit controls the base stations102 or the like; and 104 a switching station being connected with thebase station control unit 103 by wire.

Next, the operation will be explained. FIG. 2 shows conceptually anexample of a control in the direction of a receiving angle. In FIG. 2,the same reference numerals denote the same or corresponding parts. FIG.3 is a flowchart showing a flow from a tracking processing to a startingof a communication in a base station. FIG. 4 is a flowchart showing aflow from a tracking processing to a transmitting in a mobile station.FIG. 5 is a sequence diagram showing a sequence from a trackingprocessing to a communicating state between a mobile station and a basestation. In FIG. 5, a number shown in parentheses denotes an order ofthe sequence. In the present mobile radio communication system having asearching channel which controls an irradiation direction of a narrowbeam, all base stations 102 use a forward tracking channel as shown inthe prior art varying a depression angle φ and a bearing angle θ asshown in (2) of FIG. 5 and irradiates a transmitting narrow beamomnidirectionally (step S0001). Next, as shown in (3) of FIG. 5, allbase stations 102 transmit a base station identifier (hereinafterreferred to as base station ID) to identify each base station (stepS0002).

The mobile station 101 waits for a tracking channel including the basestation ID from a visiting area base station 102 as shown in (1) of FIG.5 by varying the beam receiving direction of its antenna as shown inFIG. 2 (steps S0101, S0102). In a receiver of the mobile station 101(not shown), a conventional omnidirectional receiving may be possibleaccording to parameters.

The mobile station 101 obtains a visiting area base station ID byreceiving a forward tracking channel beam from the visiting area basestation 102 (step 0103), and determines the transmitting direction shownin (4) of FIG. 5 as well as the prior art. As shown in (5) of FIG. 5,the mobile station 101 transmits a mobile station identifier(hereinafter referred to as mobile station ID) which identifies themobile station 101 in the receiving direction and a visiting area basestation ID in a reverse tracking channel (step S0105).

Further, the mobile station 101 transmits an end signal of a reversetracking channel as shown in (11) of FIG. 3 (step S0106), then uses afrequency and beam direction of a reverse tracking channel as shown in(12) of FIG. 5, and transmits by switching a tracking channel to aninformation channel (step S0107). The base station 102 similarly usesthe frequency and beam direction of the forward tracking channel inswitching to an information channel.

According to the embodiment 1 described above, after both trackingbetween the mobile station 101 and the visiting area base station 102has completed, switching to an information channel is performed usingthe same frequency and beam which are used by a tracking channel,thereby an operation switching a tracking channel to an informationchannel by another frequency and beam is not needed. Thus, aconfiguration of a device becomes more simple than a conventionalsystem.

Further, according to the embodiment 1, the visiting area base station102 varies a transmitting direction of a beam and the mobile station 101varies the receiving direction, so a receiving side may receive a beamtransmitted from the visiting area base station 102 more precisely.Thus, a receiving level of a narrow beam in the mobile station 101becomes more strong, thereby interference from the adjacent base station102 may be reduced in an area which a plurality of a base stationsoverlap.

Embodiment 2

On the other hand, when the visiting area base station 102 receives areverse tracking channel from the mobile station 101, the visiting areabase station 102 obtains the mobile station ID (step S0004), and thendetermines a transmitting direction of a beam by the same conventionalmethod as shown in (6) of FIG. 5 and halts the irradiation operation ofthe narrow beam for searching (step S0005) and irradiates a narrow beamshowing an end signal of a forward tracking channel by the forwardtracking channel to the receiving direction as shown in (7) of FIG. 5(step S0006).

Further, the visiting area base station 102 uses a frequency and a beamof a tracking channel without changing as shown in (8) of FIG. 5 totransmit an information channel (step S0007) and waits a receiving of anend signal of a reverse tracking channel from the mobile station 101 atthe same time.

When the mobile station 101 receives an end signal of a forward trackingchannel from the visiting area base station 102, it starts a receivingof a forward information channel and becomes a communication state asshown in (10) of FIG. 5.

When the visiting area station 102 receives an end signal of a reversetracking channel from the mobile station 101, it transmits a reverseinformation channel of (13) of FIG. 5. Thereby, a bidirectionalcommunication between the visiting area base station 102 and the mobilestation 101 becomes possible.

An information of a bearing angle and a receiving level is measured inany time in communication. FIGS. 6A and 6B show configurations of atracking slot and a control slot in reverse information channel f1 and aforward information channel f2. As shown in FIGS. 6A and 6B, a channelis made from some frames 200 or the like, and each frame has a searchingslot 210 or the like and followed by some control slots 214 or the likewhich transmit and receive a control signal. The information of thebearing angle and the receiving level is transmitted from the basestation 101 to the visiting area base station 102 using a control slotwhich transmits and receives a control signal shown in FIGS. 6A and 6B.The visiting area base station 102 determines an irradiation directionof a narrow beam based on the information and adjusts a control.

According to the embodiment 2 described above, after both trackingbetween the mobile station 101 and the visiting area base station 102has completed, switching to an information channel is performed usingthe same frequency and beam which are used by a tracking channel,thereby an operation switching a tracking channel to an informationchannel by another frequency and beam is not needed. Thus, aconfiguration of a device becomes more simple than a conventionalsystem.

Embodiment 3

In the embodiment 3, a case which the mobile station 101 becomes to acommunication state with the visiting area station 102 will beexplained. As shown in FIGS. 6A and 6B, an information channel betweenthe mobile station 101 and the visiting area station 102 is constitutedby a plurality of frame 200 or the like. Further, control slots 214 orthe like for controlling the mobile station 101 and the base station102, tracking slots for searching the adjacent base station 102(hereinafter referred to as searching slot) 210 or the like andinformation slots for transmitting information are provided in the frame200 or the like.

As shown in FIG. 7, while the mobile station 101 communicates with thevisiting area station 102, a searching is performed between the mobilestation 101 and the adjacent base station 102 by controlling a receivingdirection of a narrow beam at intervals of the above searching timeslots as well as the embodiment 1, and a communication of both searchingchannel is kept by the same procedure as the setting method of theinformation channel in the embodiment 2.

According to the embodiment 3 described above, as the mobile station 101can search the adjacent base station 102 although the visiting basestation 102 and the mobile station 101 are communicating each other inan overlapped area, thereby a searching time can be reduced.

Embodiment 4

FIG. 8 is a sequence diagram showing a sequence of tracking an adjacentbase station being searched. As shown in (1) of FIG. 8, adjacent basestation 104 transmits a narrow beam controlling a transmitting angle. Asshown in (2) of FIG. 8, when the mobile station 101 receives a forwardsearching slot from the adjacent base station 104 and the mobile station101 obtains the adjacent base station ID, the mobile station 101 holdsthe adjacent base station ID and a receiving direction of the ID. At thesame time, as shown in (3) of FIG. 8, the mobile station 101 transmitsthe adjacent base station ID, the receiving direction and a receivinglevel information and a control information of an information channel inthe mobile station 101 to the visiting area base station 102 incommunicating by a control slot on the information channel.

Next, as shown in (4) of FIG. 8, after the visiting area base station102 in communicating receives the above information from the mobilestation 101, it transmits the information to the base station controlunit 103. The base station control unit 103 receives the informationfrom the visiting area base station 102 and obtains the adjacent basestation ID, then as shown in (5) of FIG. 8, it transmits a beamreceiving direction, a receiving level and a control information of aninformation channel in the mobile station 101 to the adjacent basestation 104 designated by the adjacent base station ID. Thereby, theadjacent base station 104 can obtain the information, resulting in theboth tracking of the mobile station 101 and the adjacent base station104 without the tracking channel. Thus, a new tracking processing shownin (1)-(5) of FIG. 5 between the adjacent base station 104 and themobile station 101 is not necessary, thereby a tracking time can bereduced. As a switching to another frequency is not necessary, a deviceconfiguration becomes simple.

According to the embodiment 4 described above, as the mobile station 101does not transmit a reverse tracking channel to the adjacent basestation 104 and can transmit a location information using an informationchannel in communication via the visiting area base station 102, atracking time between selecting (adjacent) base station 104 and themobile station 101 can be reduced, and a device configuration becomessimple.

Embodiment 5

As shown in (6) of FIG. 8, the adjacent base station 104 which isreceived a location information of the mobile station 101 from the basestation control unit 103 halts one of irradiation operation of narrowbeams irradiated for searching the mobile station 101, and as shown in(7) of FIG. 8, transmits a beam based on the adjacent base station ID,the mobile station ID received from the base station control unit 103and a control signal to the direction of the location of the mobilestation 101 designated newly by the base station control unit 103. Acorrection of the direction is performed by controlling transmittingdirection according to the information of receiving direction as well asthe embodiment 4.

After the mobile station 101 receives the above information from theadjacent base station 104, it confirms the adjacent base station ID andthe mobile station ID by a searching slot and then transmits the mobilestation ID gain as shown in (8) of FIG. 8. Thereby, the mobile station101 can track the adjacent base station 102 in any time.

When a receiving level of a beam from the visiting area base station 104is less than a threshold value, the mobile station 101 transmits an endsignal of a searching channel to the adjacent base station 104 using theabove searching slot, and then communicates with the adjacent basestation 104 by switching the searching channel to an informationchannel. As shown in FIG. 9, by switching a plurality of informationchannels between the mobile station 101 and a plurality of the basestations 102 or the like in any time, the mobile station 101 cancommunicates with these base stations 102 or the like successively.

As shown in (1) of FIG. 10, when the mobile station 101 stopscommunication, it transmits an end signal of transmitting using acontrol slot in an information channel to the visiting area base station102 and switches a communication channel to a tracking channel.

As shown in (2) of FIG. 10, after the visiting area base station 102receives an end signal of communication from the mobile station 101, itswitches a froward communication channel to a tracking channel. At thesame time, it transmits an end signal of a forward information channelusing a forward information channel as shown in (3) of FIG. 10.

As shown in FIG. (4) of FIG. 10, after the mobile station 101 receivesan end signal of a forward information channel from the visiting areabase station 102, it switches a forward information channel to atracking channel. After that, when the mobile station 101 is in thevisiting area, the mobile station 101 transmits the mobile station IDand its location information to the visiting area station 102 as shownin (5) of FIG. 10 and performs transmitting control of the visiting areabase station 102. At the same time, it performs transmitting control ofthe mobile station 101 by transmitting the base station ID to the mobilestation 101 in a forward tracking channel.

As shown in (7) of FIG. 10, when the mobile station 101 turns off thepower or enters an area of other adjacent base station, it becomesdifficult for the visiting area base station to communicate or track themobile station 101 because the visiting area base station 102 can notdetect such situation. Therefore, a timer is set in the visiting areastation 102, thereby the timer is invoked using a receiving of alocation information as a trigger when the visiting area base station102 receives the location information of the mobile station 101 from themobile station 101. As shown in (8) of FIG. 10, the tracking channel isreleased compulsively after the timer expired, and the other mobilestation 101 is searched using the released tracking channel.

Thus, processing can proceed when the mobile station 101 turns off thepower or enters an area of other adjacent base station 102.

According to the embodiment 5 described above, as a timer is set in thevisiting area station 102 and the timer is invoked using a receiving ofa location information as a trigger from the mobile station 101 and thetracking channel is released compulsively after the timer expired andthe other mobile station 101 is searched using the released trackingchannel, thereby processing can proceed when the mobile station 101turns off the power or enters an area of other adjacent base station102.

According to the present invention, the visiting area base station 102varies a transmitting direction of a beam as well as the mobile station101 varies the receiving direction, so a receiving side may receive abeam transmitted from the visiting area base station 102 more precisely.Thus, a receiving level of a narrow beam in the mobile station 101becomes more strong, thereby a interference from the adjacent basestation 102 may be reduced in an area which a plurality of a basestation overlap.

According to the present invention, after both tracking between themobile station 101 and the visiting area base station 102 has completed,switching to an information channel is performed using the samefrequency and beam which are used by a tracking channel, thereby anoperation switching a tracking channel to an information channel byanother frequency and beam is not needed. Thus, a configuration of adevice becomes more simple than a conventional system.

According to the present invention, as the mobile station 101 can searchthe adjacent base station 102 although the visiting base station 102 andthe mobile station 101 are communicating each other by having asearching slot in an information channel, thereby a searching time canbe reduced. The searching slot is provided for searching an adjacentbase station adjacent to the visiting area base station, and thesearching slot is provided in an information channel being used incommunication between the mobile station and the visiting area station.The present invention further comprises a means for searching theadjacent base station by the mobile station using the searching slot inthe information channel and a means for transmitting a narrow beam bythe adjacent base station.

According to the present invention, as the mobile station 101 does nottransmit a reverse tracking channel to the adjacent base station 104 andcan transmit a location information using an information channel incommunication via the visiting area base station 102, a tracking timebetween selecting (adjacent) base station 104 and the mobile station 101can be reduced, and a device configuration becomes simple.

According to the present invention, as a timer is set in the visitingarea station 102 and the timer is invoked using a receiving of alocation information as a trigger from the mobile station 101 and thetracking channel is released compulsively after the timer expired andthe other mobile station 101 is searched using the released trackingchannel, thereby processing can proceed when the mobile station 101turns off the power or enters an area of other adjacent base station102.

The present invention has been described in detail with respect tovarious embodiments, and it will now be apparent from the foregoing tothose skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspects, and it isthe invention, therefore, in the appended claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

The entire disclosure of Japanese Patent Application No. 10-239721 filedon Aug. 26, 1998 including specification, claims, drawings and summaryare incorporated herein by reference in its entirety.

1. A mobile station comprising: a controller for varying the directionof reception for receiving a narrow forward tracking beam in a trackingchannel at a certain frequency, the narrow forward tracking beam beingtransmitted from at least one base station covering an area into whichthe mobile station enters, for transmitting a narrow reverse trackingbeam in the tracking channel and for varying the direction of thereverse tracking beam, wherein upon completion of a tracking process inwhich the mobile station and the at least one base station track eachother's position relative to each other using the narrow tracking beams,the mobile station and the at least one base station switch to aninformation channel using the same frequency and direction as thetracking channel.
 2. The mobile station according to claim 1, whereinthe mobile station is adapted to track an adjacent base station coveringan area adjacent to the area covered by the at least one base station byreceiving the narrow forward tracking beam of the adjacent base stationduring communication with the at least one base station.
 3. The mobilestation according to claim 2, wherein a searching slot is provided inthe information channel used by the at least one base station and themobile station, and wherein the mobile station searches for the adjacentbase station using the searching slot during communication with the atleast one base station.